In recent years, electroluminescent elements employing an organic thin film (organic electroluminescent elements) are being developed. Examples of methods for forming an organic thin film include a vacuum deposition method and a wet film formation method. Of these, the wet film formation method has advantages, for example, that no vacuum process is necessary and film formation in a larger area is easy, and that it is easy to incorporate a mixture of a plurality of materials having various functions into one layer (coating fluid).
Mainly used as the materials of luminescent layers formed by a wet film formation method are high-molecular materials such as poly(p-phenylenevinylene) derivatives and polyfluorene derivatives. However, high-molecular materials have problems including the following: (1) it is difficult to regulate the degree of polymerization and molecular weight distribution of the high-molecular materials, (2) deterioration due to residual end groups occurs during continuous drivings, and (3) it is difficult to highly purify the materials themselves and the materials contain impurities.
Due to those problems, the organic electroluminescent elements produced by a wet film formation method have poorer driving stability than organic electroluminescent elements produced by a vacuum deposition method, and have not reached a practical level at present, except some elements.
In patent document 1 is described an organic electroluminescent element employing an organic thin film formed by a wet film formation method from not a high-molecular compound but a mixture of a plurality of low-molecular materials (charge transport materials or luminescent materials) in an attempt to overcome those problems. As charge transport materials having the property of transporting holes, compounds H-1 and H-2 shown below are used therein.

Meanwhile, with respect to organic electroluminescent elements employing an organic thin film which contains a plurality of low-molecular materials and has been formed by a wet film formation method, non-patent document 1 and patent document 2 describe an organic electroluminescent element which utilizes phosphorescence so as to have enhanced luminescent efficiency. Compounds H-3, H-4, and H-5 shown below are used as charge transport materials therein.
